Spotted Bollworm on Cotton
Cotton Insect Pest SPOTTED OR SPINY BOLLWORMS
Common Name :
Spotted Or Spiny Bollworms
Local Name :
Thipkyachi, Kateri bond Ali
Scientific Name :
Earias vittella, Fabricius, 1794
E. insulana Boisd
Family :
Noctuidae
Order :
Lepidoptera
Pest Category: Lepidoptera
Description of Insect Stages:
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| Spotted Bollworm Life Cycle Stages |
Egg:
Eggs are spherical bluish-green, sculptured and less than 0.5 mm in diameter. Eggs are laid singly on most part of the cotton plant (flower buds, bolls, peduncles and bracteoles); the favored region being young shoots.
Larva:
Full-grown larva is about 1.3-1.8 cm long, stout and spindle-shaped bearing a number of long setae on each segment. The last two thoracic and all abdominal segments bear two pairs of fleshy tubercles, one of which is dorsal and the other lateral. The larva is light brown, tinged with grey to green, pale along the mid-dorsal line with dark spots at the base of tubercles of the thoracic segments. The larva of E.insulana is generally lighter in color, the pattern being grey and yellow then brown and deep orange. In E.vittella
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| Spotted Bollworm Life Cycle Stages |
Pupa:
Pupation is in a boat-shaped tough silken cocoon that is dirty, white to brownish in color. Pupae are found on plants or on fallen buds and bolls.Adult:
Adult moths differ with species. In E.insulana, the head, the thorax, and forewing color varies from silver green to straw yellow; the distal fringe of the wing is of the same color. There are three distinct transverse lines of darker shade and traces of the fourth in summer, while yellow/brown forms occur toward the end of the season. E.vittella, moths are quite distinctively creamy white or peach with a central green wedge running from proximal to the distal edge of the forewing. |
| Spotted Bollworm Eggs On Bolls |
Nature of Damage:
Neonate larvae cause damage to the terminal bud of the vegetative shoots and channel downwards or into auxiliary nodes during the early stages of crop growth. The whole apex of the main stem collapses if the main stem growing point is affected. If the apical bud alone is damaged, there is twining of the main stem due to the growth of auxiliary monopodial buds. When flower buds/bolls are attacked, the tunnel opening is blocked by excrement. Tunnel in bolls is often from below, angled to the peduncle. Larvae do not confine their feeding to a complete single boll and hence damage is disproportionate to their numbers. Damaged bolls often succumb to secondary infection by bacterial and fungal pathogens.Symptoms:
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| Square-feeding-by-Spotted-Bollworm-in-cotton |
Terminal shoots dry and withers away when the larvae
bore into the pre squaring plants. Shoots when splitting open
show downward channels with or without larvae. Feeding holes in squares and on bolls are seen with or without
larvae however blocked by excrement. A flare-up of
squares and their shedding, premature dropping or
opening of the attacked bolls are common.
Life History:
The female moth deposits 2 or 3 eggs on bracts, leaf axils
and veins on the undersurface
of a leaf. A female may lay
about 385 eggs and the incubation period is about 3 days.
The larva becomes fully grown in 10-12 days. The pupal
period is 7-10 days. The total life cycle ranges from 20-22
days. E.insulana is the most abundant species in
Northern states and E.vittella is predominant in
Peninsular India. Okra or bhindi crop provides effective
means of carrying over from one to the next season.
Seasonal Dynamics:
Square-feeding-by-Spotted-Bollworm-in-cotton
E.vittella seasonal mean damage in the rainfed cotton the production system has reached more than 10 % during
2005, being the highest in the last 5 years. E.vittella
incidence commences
as early as on 3 weeks old crop.
The number of generations up to the first flush of cotton fruiting varies among seasons, but population levels are
invariably low. Population build-up is large during the effective boll development phase of a crop causing damage
to all fruiting forms. Seasonal fluctuations of larval
populations depend upon the crop phenology in a given
year. The damage due to Earias to fruiting structures of 15-16 weeks old crop is high whenever Helicoverpa
armigera incidence is low to moderate. Never the less
beyond 20 weeks after crop emergence damage by Earias
is continuous. Earias clearly shows co-existence with H.
armigera during the early season and Pectinophora
gossypiella in the late seasons. The continuous damage to
developing bolls caused by E.vittella along with
intermittent rains leads to boll rot and results in a large
number of bolls opening with partial damage, thus
causing a reduction in yield levels.
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| Adult of Spotted Bollworm ( E.vittella ) |
Pest Management Options:
Previous season's post-harvest cultural operations such as
timely crop termination, destruction of cotton stalks and
crop residues in the fields reduce the food supply and
shelter to the bollworms. Pre planting clean up measures
during the off-season to keep the fields, their bunds and
borders free of weed hosts (esp. malvaceous plants) are a must to break the link for the pest between cotton and
alternate host crops. Bt hybrids suited to climate and soil
in areas of endemic infestations prove to be highly
effective. Pheromone traps of E.vittella and E.insulana
can be set up @ two per ha that attract male moths to
indicate the initiation and the decrease of population
development. The pheromone lures in the form of septa
are to be changed once in 45-60 days with the trap height
adjusted to 60 cm above the ground level in the early
season, and 15 cm above crop canopy in the late season.
The mechanical removal and destruction of the affected
shoots along with the larvae during the pre and early
squaring crop stage curtail the population build-up
further in the season. Managing the crop towards early
maturity decreases the period of crop susceptibility to
yield loss by bollworms. Therefore, practices that attract
more attacks by bollworms through increased vegetative
growth such as closer spacing; excessive use of systemic
insecticides during the early season for sucking pest
management and excessive nitrogen application should
be avoided. September is the month wherein Earias
spp. combined with Helicoverpa armigera cause
excessive shedding of squares. Bollworm management at
this stage should be based on the availability and damage
level to fruiting parts on the plants beside the weather. Rogas
aligarhensis parasitization on E.vittella larvae is
common on the crop that had no insecticidal spray against
sucking pests during the early crop growth phase. The use of
insecticides to be economical should commence only
when the majority of plants have at least a few flowers and set
bolls on them and the fruiting damage exceeds 10% in
relation to total fruiting structures. Mechanical collection
and destruction are advised when all the sizes of larvae
occur simultaneously. As the name indicates, bollworms
should be suppressed only when there are bolls on the
plant and boll damage is happening. The decision to spray
should be taken not based on the level of damage but
based on the retention of bolls on the crop and in
conjunction with the presence of damaging larvae on the crop. In Central, India watch should be kept on medium to
large-sized bolls during October-November months from
damage due to Earias. An average of the single larva of
Earias per plant can lead to partial damage of many bolls
resulting in bad kappas in open bolls at harvest. The
insecticides that are recommended with their dosages for
Earias management are given in the table below. E.vittella
management should be attempted with insecticides
selected from IGRs, Spinosyn, conventional (OPs, and
Carbamates) and other newer groups (Oxidiazine &
Avermectin) in rotation considering the cost of the
insecticide and anticipated level of yield saving from their
application. There should be a minimum of 10 - 15 days
interval between two sprays even at times of outbreaks to
be cost-effective.
The amount of spray fluid varies more with the canopy.
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| Recommended Insecticides for Earias Management |
size than with the crop age. It is recommended that power
sprayers are used against bollworm management through
insecticides. Normally 200-300 liters/ha of water
should be used for a crop that had attained eight to sixteen
nodes.
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